A parallel oscillator converter for inductive heating is known from the publication entitled Siemens-Zeitschrift [Siemens Journal] 45 (1971), No. 9, pp. 601-606. That device is an intermediate circuit converter circuit with an impressed current in the intermediate circuit. The direct current, which is generated by the rectifier on the power supply side from an alternating voltage in the power supply, is converted in the inverter on the load side, into a medium-frequency alternating current. The load includes an inductor, which inductively transmits the nonreactive power to the material to be heated (such as molten metal). If the high reactive power demand is to be met, the inductor must be expanded with the aid of one or more compensation capacitors to make a parallel oscillator. In the load-guided inverter, the impressed intermediate circuit current is alternatingly switched to the load at the rate of the operating frequency, through diagonally opposed valve branches, and produces approximately a sine-wave voltage in the load. Due to the load cycling, the resultant operating frequency is directly dependent on the natural frequency of the load circuit.
It is accordingly an object of the invention to provide a method for controlling the current converter valve of a load-guided parallel oscillator inverter of an induction furnace, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type and which enables an infinitely graduated adjustment or regulation of the power output to the load, or in other words to the induction furnace.